A theoretical characterization of osmotic power generation in nanofluidic systems

Abstract

Water desalination and fluid-based energy harvesting systems utilize ion-selective nanoporous materials that allow preferential transport of ions that are oppositely charged to the surface charge, resulting in the creation of an electrical current. The resultant current forms due to a potential drop or a concentration gradient (or both) applied across the system. These systems are electrically characterized by their current-voltage, $$I-V$$ , response. In particular, there are three primary characteristics: the ohmic conductance, $${G}_{{{{{\rm{Ohmic}}}}}}=I/V$$ , the zero-voltage current, $${I}_{V=0}$$ , and the zero-current voltage, $${V}_{I=0}$$ . To date, there is no known self-consistent theory for these characteristics. Here, we present simple self-consistent expressions for each of these characteristics that provide remarkable insights into the underlying physics of water desalination and energy harvesting systems. These insights can be used to interpret (and reinterpret) the numerical and experimental measurements of any nanofluidic system subject to an arbitrary concentration gradient as well as improve their design. Electrical characterization of a nanofluidic system subject to a joint potential drop and salt concentration gradient remains elusive. This work characterizes the electrical response of such systems and provides key insights into the underlying physics of nanofluidic systems.